Objective  The colonization of plant disease biocontrol agents in plant rhizosphere soil is one of the important factors affecting its biocontrol effect. In recent years, walnut anthracnose has caused serious harm to the development of walnut industry in Yunnan Province of southwestern China, and it has posed a serious threat to the development of walnut industry in the growing areas. In the early stage, Trichoderma hamatum YB-4-15 and Bacillus subtilis yb33, which are important biocontrol agents, were obtained indoors by screening biocontrol of anthracnose on walnut in rhizosphere soil of Guangming Village, Yangbi County, Dali City. To better promote the above biocontrol agents, the colonization of the above strains in the rhizosphere of walnuts should be firstly considered.

  Method  Trichoderma spore suspensions of different concentrations were applied to sterilized rhizosphere of walnuts.

  Result  The colonization amount of the two biocontrol agents in rhizosphere soil was regularly measured, and it was found that after one month of mixing the biocontrol agents to the rhizosphere soil, the colonization amount of T. hamatum was 2 × 10⁴ cfu/g at lowest level to 5 × 10⁴ cfu/g at maximum level. At the same time, the rifampicin-resistant B. subtilis yb33-Rif was used to determine the colonization ability in sterilized soil and field soil, the colonization amount of tested bacteria ranged from 7.07 × 10⁶ to 1.08 × 10⁸ cfu/g, significantly lower in field soil than in sterilized soil, ranging from 1.03 × 10⁶ cfu/g at lowest level to 7.53 × 10⁶ cfu/g at maximum level. In addition, the two tested biocontrol agents were mixed in the rhizosphere soils of walnut, osmanthus, camphor and heather, and it was found that the two biocontrol agents were found to grow well in walnut rhizosphere soil.

  Conclusion  The current study lays a solid base for future application of the two biocontrol agents in walnut fields.